In a digital projection system, an image-bearing light beam is generated from a light source and ultimately cast onto a viewing surface. The light source commonly includes a mercury lamp, or other light filament, that is fixed within a reflective housing. The light source generates a light beam having wavelengths in the ultra-violet (UV), infrared (IR), and visible (VIS) ranges. In known projection systems, the housing is commonly made from glass and is coated with a reflective multi-layer optical coating that is designed to reflect light in the VIS range. Whether stray light from the light beam is reflected, absorbed, or transmitted through the light source is dependent on the type of incident light. For example, in some known reflectors stray light in the VIS range is generally reflected from the optical coating back into the light beam. Stray light in the UV and IR range, on the other hand, is generally absorbed by the glass housing or is transmitted into the projection system. However, it is advantageous for all of the UV and IR light to be absorbed by the reflective housing because stray light that is not absorbed generates excess heat in the projection system, requiring additional cooling mechanisms.
The embodiments described hereinafter were developed in light of this and other drawbacks associated with known glass reflectors in digital projection systems.